2970N2 help

[n4dxx]

Have a rather new rci 2970n2 mosfet and it has the feedback suppressors installed but still have excessive current draw like 15 amps on key and 40 amps peak and feedback when you unkey the mike..Like self ocs..and does it as well sometimes when you turn the rig on..the more you use it the less it happens.Radio sounds loud and clear just noise on the recieve sometimes when the mike is unkeyed.Any ideas?

 

[9C1Driver]

In some of the older N2 threads this was talked about, guys were having to run a 52 amp power supply with it. I think Dave at DTB would correct this problem. Someone will chime in on the exact issue I am sure.

 

[Mudfoot]

It sounds like it has a hotrod tune. It wouldn't be surprising if it was oscillating as well. Give it an alignment to within factory specs. This should help the receive as well.

Anyway, the alignment results would determine my next move.

 

[n4dxx]

It sounds like it has a hotrod tune. It wouldn't be surprising if it was oscillating as well. Give it an alignment to within factory specs. This should help the receive as well.

Anyway, the alignment results would determine my next move.

Thats the problem when i unkey the mike and sometimes when i just power up the rig the s-meter will peg out and make a static noise sounds like its oscillating and getting into the receivers front end..sounds like a lightning storm at times..any adjustment in paticular that i need to check?..Thanks

 

[n4dxx]

I know this is a dead horse but i still have the same radio with the same problem..Need some help here..Thanks

 

[ExitThirteen]

The N2's are a junk radio.... now that I have gotten that statement out of the way, I'm willing to bet the biasing on the PA board is set way too high. That was a problem that Ranger had in a lot of the N2's... they had so many come back to to them because of excessive current draw/oscillation issues and blown up PA boards.

Best way to check for biasing on the PA board is to check the gate voltage on the 8 mosfets. They should be around 4-4.5V or so. If it's higher, you'll need to adjust the bias voltage back down. That "can" be part of the issue you are having.

~Cheers~

 

[n4dxx]

Thanks i will check that..report my findings

 

[ExitThirteen]

Yep, let us know where the gate voltages are at.... I've had some N2's come across my bench that were close to 6 volts at the gates of the mosfets. SIX VOLTS. That's insanely high for IRF520's. For linear amp applications, you could go as high as 4.5V and get away with it, provided you don't push them real hard. I'd recommend going 4.1-4.2V so you don't cook them.


~Cheers~

 

[n4dxx]

Yep, let us know where the gate voltages are at.... I've had some N2's come across my bench that were close to 6 volts at the gates of the mosfets. SIX VOLTS. That's insanely high for IRF520's. For linear amp applications, you could go as high as 4.5V and get away with it, provided you don't push them real hard. I'd recommend going 4.1-4.2V so you don't cook them.


~Cheers~

How about just the opposite all of my settings are less than 3vdc to be exact 2.85 or less on all Gates measured with a wavetek 10XL

 

[ExitThirteen]

Oh wow, that's strange. They should be much higher than that. Set them to about 4V and see if that helps. That's close to where they are supposed to be. They can be set at VR2 and VR3.


~Cheers~

 

[n4dxx]

Oh wow, that's strange. They should be much higher than that. Set them to about 4V and see if that helps. That's close to where they are supposed to be. They can be set at VR2 and VR3.


~Cheers~

Yes as far as i can tell it has took care of the issue..Now i need to set the main board drivers they are also at less than 3 volts..I can't thank you enough for leading me in the right direction..I think you nailed it..

 

[ExitThirteen]

Ok, on the main board, the driver should be set at about 3.75V at the gate, the finals should be set about 3.5-3.6V at the gates.

~Cheers~

 

[Robb]

Didn't think that the 520 could handle more than 5v.
Thought the standard setting for it was 4v/slightly less?

 

[n4dxx]

Ok, on the main board, the driver should be set at about 3.75V at the gate, the finals should be set about 3.5-3.6V at the gates.

~Cheers~

Real quick do you know the VR's for the main board?Don't have service manual

 

[ExitThirteen]

If memory serves me right, VR13 is your driver bias, VR11 and VR12 are your final bias. Just look for a small trimmer pot next to each mosfet on the main PCB. I believe those are the numbers you're after, tho.


~Cheers~